Fog Unit?? I think you have H3 globes in the fog lights, not HID. Change the H3 globes. Stick to 55w. Use +x% output if you want to. If you do have HID (not to be confused with xenon globes) then I belive they will be aftermarket by a PO..
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 White and 1 Light Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i